An automotive steering box is typically located at the terminus of the steering wheel shaft, and converts the rotation of the steering wheel into the primarily linear movement of a steering arm, with the steering arm coupled to the steering components of the automobile. The steering components are typically attached to the front wheels of the vehicle, and the front wheels are coupled to suspension components. One example prior art steering box utilizes a worm gear coupled through one or more pins to drive a rotating plate with the worm gear providing gear reduction and the worm gear driven by a shaft coupled to the steering wheel. Such worm-gear steering systems were manufactured by the Ross Corporation and commonly used in Kaiser Willys, Studebaker, and similar early vehicles.
In one example device manufactured by the Ross Corporation, the rotating plate is coupled to the worm gear using two tapered pins which engage with the helically cut tooth of a worm gear. When the steering wheel is rotated, this rotation is coupled via universal joints to the steering box worm gear, which causes the pins to follow an arc trajectory described by the rotating plate axis and tapered pin engagement with the worm gear. One or two (or more) tapered pins may be attached to the rotating plate and engage with the worm gear. While some steering systems use one pin, two pins are typically used to distribute the load to the steering link, to enable a greater angular rotation control at the extremities of rotation when one pin reaches the end of engagement with the worm gear, and to reduce free movement or “play” in the steering system by distributing the wear to two pins, and provide for a redundant system for safety purposes.
Although steering systems are heavily lubricated with grease, significant wear occurs on the contact surfaces of the pins and worm gear, and as the tapered pins and worm gear wear, the free movement or “play” increases which introduces steering error and shimmy into the steering system, either of which can pose a hazardous condition for the vehicle, driver, and any passengers.
Additionally, wear is concentrated in areas of the worm gear where the pin surfaces are most frequently in wear contact with the worm gear, and less wear is associated with regions of the worm gear where the worm gear and pin engagement is less common. The worn regions of the worm gear and pins typically correspond to the rotational position of the worm gear associated with driving straight ahead, and the “unworn” regions of the worm gear reference the less frequently used regions, such as those corresponding with a turning position of the steering wheel. In the present description, “worn region” also refers to regions of the worm gear where the pin and worm gear surfaces which have increased play, and “unworn region” also refers to regions of the worm gear with less-worn regions than the worn regions, such as those associated with a turning position of the steering wheel. As the rotating plate, or steering link, coupled to the pins turns, the rotation of the steering link likewise rotates the tapered pins which causes different faces of the tapered pins to mate with the worm gear, but because the steering wheel is typically held in the straight-ahead position more often than it is held in the turning position, the “worn region” is found on the faces of the tapered pins and worm gear surfaces which contact each other in the straight-ahead steering position to a greater extent than the turning position of the steering wheel. If the conventional adjustment screw of a prior art steering box is tightened to reduce the play between the pins and worm gear by pressing the tapered pins further into engagement with the worm gear, the adjustment will reduce play produced by wear on the tapered pins at the worn regions, but introduce binding of the full turning of the worm gear when the non-worn faces of the tapered pins are rotated and come in contact with the unworn regions of the worm gear, which binding can contribute to or cause loss of steering control. Additionally, the conventional adjustment screw does not include provisions for failure protection, such as where the adjustment screw works loose from the steering box, in which event a very large level of pin movement perpendicular to the worm gear axis is possible.
It is desired to provide a worm gear steering box which eliminates play associated with region-specific wear patterns. It is also desired to provide an adjustment screw which provides sufficiently constant pressure on the pins engaged with the worm gear to maintain the engagement of the pins into the associated worm gear through its entire range of motion. It is also desired to provide an adjustment screw which minimizes the amount of displacement of the pins away from the worm gear in the event of a failure in the adjustment screw.